Crosslinked actin networks show liquid crystal elastomer behaviour, including soft-mode elasticity

Actin filament networks with protein crosslinks of distinct length and flexibility resemble liquid crystal elastomers. We simulate actin. lament systems with flexible crosslinkers of varying length and connectivity to understand general phase behaviour and elasticity. Simulated networks with very short. laments and long crosslinkers resemble the cytoskeleton of the red blood cell and remain isotropic in compression and shear, seeming well-suited to blood flow. In contrast, networks with longer. laments as found in many cell types show three regimes of nematic phase behaviour dependent on crosslinker length: ( 1) 'loose' networks are isotropic at zero stress but align under compression or shear; ( 2) 'semi-loose' networks are nematic at low stress but become isotropic under dilation and ( 3) 'tight' networks possess a locked-in nematic order as represented by the cytoskeleton of the outer hair cell in the ear, for which anisotropic compliance directs sound propagation. Furthermore, for a subset of loose networks with 'periodic' connections among. laments, extremely soft stress - strain behaviour is found, as predicted for liquid crystal elastomers.